1. Field of the Invention
The present invention relates to a non-invasive blood analyzer and provides an apparatus for transcutaneously measuring a size of a blood vessel, a blood component concentration and a blood component concentration ratio in real time with excellent reproducibility without exsanguinating blood.
2. Description of the Related Arts
A method of directly measuring a blood vessel width by using images has been carried out with microcirculation (particularly at blood vessel on retina) as an object (refer to, for example, M. J. DEVANEY et al., "Continuous Measurement of Vascular Diameters via Television Microscopy", ISA TRANSACTION, Vol. 15, No. 1, pp. 73-78, 1976). However, according to the method, a blood vessel of several tens .mu.m is measured as an object and accordingly, the method is not suitable for actual clinical use.
Further, an apparatus for measuring transcutaneously a hemoglobin concentration and a hematocrit has been devised. For example, there has been disclosed an apparatus of irradiating a plurality of wavelengths of light to a human body and measuring hemoglobin in blood from a change in an optical intensity caused by pulsation in "Hemoglobin concentration measuring apparatus" (Japanese Examined Patent Publication No. JP-B-3-71135). Similarly, there has been disclosed a method of calculating a hematocrit in blood by utilizing pulsation or the like in "System and method for non-invasive hematocrit monitoring" (U.S. Pat. No. 5,372,136).
However, these publications pose a problem in accurately calculating an absolute value, since an amount of blood for constituting an object of inspection is not specified. Further, it is anticipated that a difference is caused in measured value depending on a portion of the living body for mounting a sensor which is problematic in view of reproducibility or the like.
Further, although there has been disclosed a method of measuring the above-described items from images of red corpuscles flowing in a capillary in "Apparatus and method for in vivo analysis of RED and WHITE blood cell indices" (U.S. Pat. No. 4,998,533), according to the method, the system is extremely large-scaled.
Also, various non-invasive blood analyzers such as shown below are known. For example, an apparatus in which an image of an inside region of a blood vessel contained in a portion of a living body is captured to analyze the morphology and the number of blood cells from the obtained image (See U.S. Pat. No. 5,598,842 or Japanese Unexamined Patent Publication No. HEI 7(1995)-308312), an apparatus in which images of a blood vessel contained in a portion of a living body are captured by a plural number of times to determine a differential image thereof for detecting a blood cell image (See Japanese Unexamined Patent Publication No. HEI 7(1995)-308311), an apparatus provided with means for searching a blood vessel of a desired size contained in a portion of a living body by mechanically moving a transparent plate positioned in close contact with a skin surface of the living body so as to capture an image of the blood vessel through the transparent plate (See Japanese Unexamined Patent Publication No. HEI 8(1996)-299310), an apparatus in which an image of a blood vessel and a tissue contained in a portion of a living body is captured to calculate an amount of a blood component from an image density distribution distributed across the blood vessel in the captured image (See Published International Patent Application Number WO 97/24066) and the like are known.
Here, if images of a portion of a living body are to be captured time-sequentially by means of such a non-invasive blood analyzer to find a time-sequential change of an analysis value, an image capturing apparatus is separated from the living body after an image of the portion of the living body has been captured and, after several hours or several days, an image of the portion of the living body is captured again. However, since the reproducibility of the blood vessel portion whose images are to be captured is not ensured, it is difficult to obtain an analysis value accurately with respect to the same blood vessel portion.